Capacitive sensor for a digitizer system

Abstract

A pressure sensitive capacitive sensor for a digitizer system includes an interaction surface over which a user interacts with the capacitive sensor, at least one sensing layer operable to sense interaction by mutual capacitive sensing, the at least one sensing layer extending across the interaction surface, and an additional layer comprising resilient properties and operable to be locally compressed responsive to pressure locally applied on the interaction surface during user interaction with the capacitive sensor.

What is claimed is: 
     
         1 . A pressure sensitive capacitive sensor for a digitizer system, the capacitive sensor comprising:
 an interaction surface over which a user interacts with the capacitive sensor;   at least one sensing layer operable to sense interaction by mutual capacitive sensing, the at least one sensing layer extending across the interaction surface, wherein the at least one sensing layer is patterned with row and column sensing strips arranged in a grid; and   an additional layer comprising resilient properties and operable to be locally compressed responsive to pressure locally applied on the interaction surface during user interaction with the capacitive sensor.   
     
     
         2 . The capacitive sensor according to  claim 1  wherein the additional layer is selected to have a hardness of between 20-70 shore A and thickness of between 50-500 μm. 
     
     
         3 . The capacitive sensor according to  claim 1 , comprising a protective layer, wherein the interaction surface is a surface of the protective layer, wherein the protective layer is formed from flexible material that is operable to bend responsive to pressure locally applied on the interaction surface. 
     
     
         4 . The capacitive sensor according to  claim 1 , comprising a rigid layer, wherein the rigid layer is positioned distal from the interaction surface and wherein the additional layer is positioned between the rigid layer and the at least one sensing layer. 
     
     
         5 . The capacitive sensor according to  claim 4 , wherein the rigid layer is formed from a glass substrate. 
     
     
         6 . The capacitive sensor according to  claim 1 , comprising a reference layer, wherein the reference layer is conductive and is connected to ground or to a reference voltage, and wherein the additional layer is positioned between the at least one sensing layer and the reference layer. 
     
     
         7 . The capacitive sensor according to  claim 1 , wherein the at least one sensing layer is a single sensing layer and wherein the single sensing layer is formed with a flexible that is operable to bend responsive to pressure locally applied on the interaction surface. 
     
     
         8 . The capacitive sensor according to  claim 1 , wherein the at least one sensing layer includes a first sensing layer patterned with row conductive strips and a second sensing layer patterned with column conductive strips and wherein the additional layer is positioned between the first sensing layer and the second sensing layer. 
     
     
         9 . The capacitive sensor according to  claim 8 , wherein at least one of the first and second sensing layers is formed with a flexible material and is operable to bend responsive to pressure locally applied on the interaction surface. 
     
     
         10 . The capacitive sensor according to  claim 9 , wherein the additional layer is operative to provide for locally reducing distance between the first and second sensing layer, wherein the reducing is responsive to the applied pressure during the interaction. 
     
     
         11 . The capacitive sensor according to  claim 1 , wherein the at least sensing layer of the capacitive sensor is retrofitted with the additional layer. 
     
     
         12 . The capacitive sensor according to  claim 1 , wherein the additional layer is formed from a transparent material that is non-conductive. 
     
     
         13 . A digitizer system comprising:
 a capacitive sensor according to any one of  claim 1 , and   circuitry electrically connected to the capacitive sensor, wherein the circuitry is adapted for detecting output from the capacitive sensor and for determining both location of an interaction and pressure applied at the interaction location responsive to the output.   
     
     
         14 . A pressure sensitive touch screen comprising:
 an interaction surface over which a user interacts with the touch screen;   at least one sensing layer operable to sense interaction by mutual capacitive sensing, the at least one sensing layer extending across the interaction surface, wherein the at least one sensing layer is patterned with row and column sensing strips arranged in a grid;   an additional layer comprising resilient properties and operable to be locally compressed responsive to pressure locally applied on the interaction surface; and   a flat panel display.   
     
     
         15 . The touch screen according to  claim 14  wherein the additional layer is selected to have a hardness of between 20-70 shore A and thickness of between 50-500 μm. 
     
     
         16 . The touch screen according to  claim 14 , wherein the interaction surface is formed by a protective layer positioned over the at least one sensing layer, wherein the protective layer is formed from flexible material that is operable to bend to responsive to pressure locally applied on the interaction surface. 
     
     
         17 . The touch screen according to  claim 14 , wherein the additional layer is positioned between the at least one sensing layer and the flat panel display. 
     
     
         18 . The touch screen according to  claim 14 , comprising a reference layer, wherein the reference layer is conductive and is connected to ground or to a reference voltage and wherein the additional layer is positioned between the at least one sensing layer and the reference layer. 
     
     
         19 . The touch screen according to  claim 14 , wherein the touch screen is retrofitted with the additional layer. 
     
     
         20 . A method for sensing applied pressure with a capacitive sensor that includes a resilient layer, the method comprising:
 scan output from a capacitive sensor;   identify an interaction point;   detect pressure profile around the interaction point; and   determine pressure applied at the interaction point responsive to a feature of the detected pressure profile.   
     
     
         21 . The method according to  claim 20 , wherein the feature is a gradient of the pressure profile around the interaction point. 
     
     
         22 . The method according to  claim 20 , wherein the pressure profile is detected in a frequency band used to interrogate the capacitive sensor during scanning. 
     
     
         23 . The method according to  claim 20 , wherein the interaction point is responsive to touch by at least one of a fingertip and stylus. 
     
     
         24 . The method according to  claim 20 , wherein the pressure profile and the location of the interaction points are detected in different time frames.